Wireless tissue electrostimulation

ABSTRACT

A wireless electrostimulation system can comprise a wireless energy transmission source, and an implantable cardiovascular wireless electrostimulation node. A receiver circuit comprising an inductive antenna can be configured to capture magnetic energy to generate a tissue electrostimulation. A tissue electrostimulation circuit, coupled to the receiver circuit, can be configured to deliver energy captured by the receiver circuit as a tissue electrostimulation waveform. Delivery of tissue electrostimulation can be initiated by a therapy control unit.

CLAIM OF PRIORITY

This patent application is a continuation of U.S. application Ser. No.14/264,663 filed on Apr. 29, 2014, now U.S. Pat. No. 9,393,405, which isa continuation of U.S. application Ser. No. 12/361,884, filed on Jan.29, 2009, which claims benefit to U.S. Provisional Patent ApplicationNo. 61/059,993 filed on Jun. 9, 2008 and to U. S. Provisional PatentApplication No. 61/063,876 filed on Feb. 7, 2008, all of which arehereby incorporated by reference in their entirety.

CROSS-REFERENCE TO RELATED PATENT DOCUMENTS

This patent application is related to U.S. patent application Ser. No.11/854,844, entitled “Cardiac Stimulation Using Leadless ElectrodeAssemblies,” filed on Sep. 13, 2007 (Attorney Docket No. 279.G03US1),now issued as U.S. Pat. No. 8,644,934, and U.S. patent application Ser.No. 11/511,152, entitled “Cardiac Stimulation System,” filed on Aug. 28,2006 (Attorney Docket No. 279.F96US1), now issued as U.S. Pat. No.7,848,823, the entire contents of both of which are incorporated hereinby reference.

BACKGROUND

A variety of therapeutically-useful intra-body electrostimulationtechniques have been employed by physicians to treat both acute andchronic patient conditions. Electrostimulation of soft muscle tissue maybe used, for instance, to elicit contractile behavior, or to inhibitsuch contractile activation.

In particular, electrostimulation is commonly used for cardiac rhythmmanagement. Cardiac rhythm management devices include, for example,pacemakers, cardiac resynchronization therapy devices, and cardioverterdefibrillators. Cardiac rhythm management devices can be used to treatconditions such as atrial or ventricular tachycardia, atrial orventricular fibrillation, bradycardia, and congestive heart failure.

An example of an application of a cardiac rhythm management deviceincludes a battery-operated pulse-generator assembly subcutaneouslyimplanted in the pectoral region, connected to one or more implantableleads deployed through the vasculature using a catheter-based deliverysystem to locations either within one or more of the heart chambers, orwithin one of the great veins of the heart.

Implantable flexible leads include one or more exposed electrodes todirectly stimulate cardiac tissue, or to sense potentials developedacross the electrodes by the tissue (e.g., for sensing intrinsic cardiacactivity, or sensing the evoked response to the application ofelectrostimulus). Tissue growth occurs, and frequently surrounds thearea of the electrode in contact with tissue. This may result in thebeneficial effect of reducing the required electrostimulus threshold toachieve the desired response, but also presents challenges should thenecessity arise to re-position or remove the lead. This may preclude theusage of multiple leads in certain locations.

Epicardial stimulus locations are also sometimes used, for instanceduring times when acute pacing therapy is desired, associated with othermedical procedures, and where access is easily obtained to thepericardial cavity.

OVERVIEW

Some conditions, such as congestive heart failure, benefit from pacingat multiple cardiac sites in a specially timed manner, including pacingat a right-ventricular site, and one or more left-ventricular sites.

Generally, leads are contra-indicated in the left heart chambers due tothe risk of thrombo-embolism. Also, risk exists of mechanicaldislodgement, due to the more significant motions, acceleration andimpingement of cardiac tissue on the lead and electrode assembly, if alead system is implanted endocardially in the left ventricle or leftatrium.

For the reasons above, left-ventricular pacing is typically accomplishedfrom a venous site. However, the risk of obstructing a significantproportion of the venous cross section is great, compromising bloodsupply to myocardium. It can be difficult to pace at more than one leftventricular site. Additionally, the efficiency of pacing at a venoussite can be correspondingly less desirable than an intra-chamberlocation such as the left-ventricular free wall (e.g., the requiredpacing energy level to elicit reliable activation or “capture,” can behigher at the venous site than at a corresponding endocardial locationwherein the electrode is directly implanted in the myocardium). Thecomplexity of lead removal and the limited available area can precludethe usage of multiple leads to achieve multiple stimulation sites in theleft heart.

Wireless pacing electrodes can eliminate the need for the wiredconnection between the pulse generator assembly and an electrodeassembly at a pacing site, since such wireless assemblies can fitentirely within a heart chamber, at an endocardial location. Generally,pacing energy is supplied to the tissue from a tiny rechargeable batterylocated in the body of the wireless pacing electrode. Such a design hasthe advantage of enabling an autonomous pacing assembly, but sizeconsiderations can result in frequent (e.g., daily) battery recharge viamagnetic induction. Further, the construction of various wireless pacingdevices using materials with high magnetic permeability, such asferrite-core inductors, can present a compatibility problem withmagnetic resonance imaging (MRI) equipment.

By contrast, among other things, the present system in certain examplescan provide electrostimulation at patient implant locations, such as anendocardial location, where usage of lead-wire systems is problematic,and wherein stimulation is desired at multiple sites separate anddistinct from the location of a therapy control unit and wireless energysource.

The present system in certain examples can also improve useful wirelesscommunication range to, for example, several centimeters in cardiacpacing or other electrostimulation applications, using one or moreinductors including a core material having a lower relative magneticpermeability than ferrite, or substantially equal to 1 (e.g., such asair, body tissue, bodily fluids, or one or more other media), or using atuned receiver design. Multiple receivers can be driven by a singleinductive transmit antenna with limited loss in efficiency, as comparedto a single receiver.

The inductive transmit antenna can be located either subcutaneouslywithin the patient or included with an external device, such as ahospital bed, operating table, hand-held device, hat or clothing, forexample.

In the case of a subcutaneously-implanted therapy control unit andinductive transmitter (such as a cardiac rhythm management device),explant might be required to replace the battery. Enhanced efficiencyfrom resonant coupling or larger air-core loop inductive antennastructures can facilitate increased operating time between rechargeoperations or battery replacement.

In the case of an external inductive transmitter, a greater distancebetween the transmitter and wireless electrostimulation node “seed”devices can be achieved.

The wireless electrostimulation node “seed” device can be implanted at acardiac location, such as endocardially, entirely within a heartchamber, and can be configured with an expandable inductive loopantenna. During the implantation procedure, the expandable loop can beinitially collapsed or folded to allow easier implant, and then unfoldedor expanded to achieve a larger surface area, and hence greater couplingto the inductive transmit antenna. In a cardiac pacing example, aninductive transmit antenna can be incorporated into a cardiac leadsystem and can be configured to expand or unfold once implanted in adesired location.

In an example, a wireless electrostimulation system can include awireless energy transmission source, and an implantable cardiovascularwireless electrostimulation node. In an example, a receiver circuit caninclude an inductive antenna, and the antenna can be configured tocapture magnetic energy to generate a tissue electrostimulation. In anexample, a tissue electrostimulation circuit, coupled to the receivercircuit, can be configured to deliver energy captured by the receivercircuit as a tissue electrostimulation waveform, without requiring adiscrete capacitor or electrochemical storage (e.g., a battery, acapacitor using bodily fluid or tissue as an electrolyte, or one or moreother storage devices) on-board or conductively coupled to the receivercircuit. In an example, delivery of tissue electrostimulation can beinitiated by a therapy control unit.

Example 1 comprises a wireless electrostimulation system. In thisexample, the system includes: a wireless energy transmission source,including an inductive antenna, configured to generate a time-varyingmagnetic flux; a cardiovascular wireless electrostimulation node sizedand shaped to be implantable using a percutaneous transluminal catheterdelivery system, the wireless electrostimulation node comprising: areceiver circuit configured to capture at least enoughinductively-coupled energy from the inductive antenna to generate atissue electrostimulation, the receiver circuit comprising amechanically-expandable inductive pickup configured to link thetime-varying magnetic flux, the inductive pickup comprising a corematerial including a relative magnetic permeability less than 1.1; atissue electrostimulation circuit, coupled to the receiver circuit,configured to deliver energy captured by the receiver circuit as aspecified tissue electrostimulation waveform, the tissueelectrostimulation circuit comprising at least one tissueelectrostimulation electrode; and a therapy control unit,communicatively coupled to the tissue electrostimulation node andconfigured to initiate a delivery of a tissue electrostimulation by thetissue electrostimulation electrode.

In Example 2, the system of Example 1 optionally comprises a systemwherein the cardiovascular wireless electrostimulation node isconfigured and sized for intravascular delivery.

In Example 3, the system of at least one of Examples 1-2 optionallycomprises a system wherein the receiver circuit comprises: an energystorage device configured to store inductively-coupled energytransferred by the time-varying magnetic flux; wherein the energystorage device is configured to store at most 1 milliJoule of energy;and wherein the tissue electrostimulation is inhibited by a depletion ofthe energy storage device no more than 1 minute after the termination ofthe inductively-coupled energy transfer.

In Example 4, the system of at least one of Examples 1-3 optionallycomprises a system wherein the tissue electrostimulation circuitcomprises: a rectifier, coupled between the receiver circuit and thetissue stimulation electrode; a direct-current blocking device, coupledbetween the tissue electrostimulation electrode and the receivercircuit; wherein the at least one tissue electrostimulation electrodecomprises a cathode configured to be coupled to cardiac tissue; whereinthe at least one tissue electrostimulation electrode comprises an anodeconfigured to be coupled to cardiac tissue; and wherein the tissueelectrostimulation circuit is configured to be capable of generating,between the anode and the cathode, an electrostimulation pulse of atleast 2.5V peak amplitude at a pulse width of 0.4 msec when coupled to a500 Ohm equivalent load.

In Example 5, the system of at least one of Examples 1-4 optionallycomprises: a mechanically-expandable inductive pickup comprising: aninsulated wire loop; an expandable mechanical support comprising a loopof shape-memory material mechanically coupled to the insulated wireloop, wherein at least a portion of the loop of shape-memory material isnon-conductive; a housing comprising: a receiver circuit electricalcharge storage device conductively coupled to the insulated wire loop;the tissue electrostimulation circuit; wherein the housing is disposedwithin a space encompassed by the loop of shape-memory material; and astrut, comprised of shape-memory material, configured to secure the loopof shape-memory material to the cylindrical housing.

In Example 6, the system of at least one of Examples 1-5 optionallycomprises a bio-compatible dielectric encapsulant configured toencompass at least a portion of the inductive pickup.

In Example 7, the system of at least one of Examples 1-6 optionallycomprises a system wherein the wireless energy transmission source isconfigured to vary a burst pulse duration of the time-varying magneticflux, wherein the tissue electrostimulation circuit comprises a voltageclamping device coupled to the output of the rectifier, and wherein theenergy content of the electrostimulation pulse is controlled by theburst pulse duration when a voltage across the voltage clamping deviceis substantially equal to or greater than a voltage clamping devicethreshold voltage.

In Example 8, the system of at least one of Examples 1-7 optionallycomprises a system wherein the inductive pickup is configured for amaximum outside diameter, when expanded, of less than or equal to 2 cm;wherein the housing comprises a cylindrical diameter less than or equalto 2 mm, and a length less than or equal to 5 mm; and wherein a totallength of the cylindrical housing and the cardiac tissue attachmentmechanism is less than or equal to a nominal minimum myocardial tissuewall thickness of 10 mm.

In Example 9, the system of at least one of Examples 1-8 optionallycomprises a system wherein the wireless energy transmission source isconfigured to generate the time-varying magnetic flux at a specifiedreceiver resonant frequency within a range of frequencies from 500kilohertz to 5 megahertz, inclusive; and wherein the wireless energytransmission source is configured to deliver the inductively coupledenergy at a power coupling efficiency of at least 1%.

In Example 10, the system of at least one of Examples 1-9 optionallycomprises a system wherein the wireless energy transmission source andthe therapy control unit are both configured to be located external to apatient's body containing the wireless electrostimulation node.

In Example 11, the system of at least one of Examples 1-10 optionallycomprises a battery-powered implantable cardiac rhythm management unitthat includes the wireless energy transmission source and the therapycontrol unit.

In Example 12, the system of at least one of Examples 1-11 optionallycomprises a system wherein the wireless energy transmission sourcecomprises: an implantable flexible lead comprising: a distal endconfigured to be located near the implantable wirelesselectrostimulation node; a proximal end configured to be located at ornear a housing of the battery-powered implantable cardiac rhythmmanagement unit; at least two antenna feed conductors disposedinternally to the lead and conductively coupled to the housing of thebattery-powered implantable cardiac rhythm management unit; theinductive antenna disposed at the distal end of the lead, andconductively coupled to the at least two antenna feed conductors at thedistal end of the lead; and the therapy control unit configured toenergize the at least two antenna feed conductors.

Example 13 describes a method. In this example, the method comprises:delivering a cardiovascular wireless electrostimulation node to anintra-body location; expanding a wireless electrostimulation nodeinductive pickup; generating a time-varying magnetic flux; linking thetime-varying magnetic flux to the wireless electrostimulation nodeinductive pickup; configuring a wireless electrostimulation nodeinductive pickup wire loop with a core material of a relative magneticpermeability less than 1.1; capturing at least enoughinductively-coupled energy to deliver a tissue electrostimulation;controlling the initiation of the delivery of a specified tissueelectrostimulation waveform; and delivering a specified tissueelectrostimulation waveform in response to an initiation.

In Example 14, the method of Example 13 optionally comprises deliveringa cardiovascular wireless electrostimulation node through a vascularpath to an intra-body location.

In Example 15, the method of at least one of Examples 13-14 optionallycomprises: storing the inductively-coupled energy within an energystorage device included in the wireless electrostimulation node;inhibiting the storage of more than 1 milliJoule of energy within theenergy storage device; terminating the time-varying magnetic flux;depleting the energy storage device; and inhibiting the delivery of thetissue electrostimulation more than 1 minute after the termination ofthe time-varying magnetic flux in response to the depleting the energystorage device.

In Example 16, the method of at least one of Examples 13-15 optionallycomprises: rectifying the time-varying magnetic flux; coupling a cathodeto cardiac tissue; coupling an anode to cardiac tissue; generating,between the anode and the cathode, an electrostimulation pulse of atleast 2.5V peak amplitude at a pulse width of 0.4 msec when coupled to a500 Ohm equivalent load; and blocking the passage of direct-currentbetween a tissue stimulation electrode and a receiver circuit.

In Example 17, the method of at least one of Examples 13-16 optionallycomprises: insulating the inductive pickup wire loop; coupling theinductive pickup wire loop to a shape-memory mechanical supportmechanically; expanding the shape-memory expandable mechanical supportto a specified loop shape proximate to a cardiac tissue wall; forming anon-conductive portion along the circumference of the shape-memoryexpandable mechanical support; coupling the shape-memory mechanicalsupport to a cylindrical housing mechanically; and disposing thecylindrical housing within a space encompassed by the shape-memorymechanical support.

In Example 18, the method of at least one of Examples 13-17 optionallycomprises: encompassing at least a portion of the inductive pickup witha bio-compatible dielectric encapsulant.

In Example 19, the method of at least one of Examples 13-18 optionallycomprises: varying a burst pulse duration of the time-varying magneticflux; clamping a voltage developed by the rectifying the time-varyingmagnetic flux; and

controlling the energy content of the electrostimulation pulse, via thevarying of the burst pulse duration of the time-varying magnetic flux,when a voltage across a voltage clamping device is substantially equalto or greater than a voltage clamping device threshold voltage.

In Example 20, the method of at least one of Examples 13-19 optionallycomprises: expanding the inductive pickup to a maximum outside diameter,when expanded, of less than or equal to 2 cm; limiting the cylindricalhousing to a diameter less than or equal to 2 mm; limiting thecylindrical housing to a length less than or equal to 5 mm; and limitinga total length of the cylindrical housing and a cardiac tissueattachment mechanism to less than or equal to a nominal minimummyocardial tissue wall thickness of 10mm.

In Example 21, the method of at least one of Examples 13-20 optionallycomprises: generating the time-varying magnetic flux at a specifiedreceiver resonant frequency within a range of frequencies from 500kilohertz to 5 megahertz, inclusive; and transferring theinductively-coupled energy at a power coupling efficiency of at least1%.

In Example 22, the method of at least one of Examples 13-21 optionallycomprises: generating the time-varying magnetic flux from a locationexternal to a patient's body; and initiating a tissue electrostimulationfrom a location external to the patient's body.

In Example 23, the method of at least one of Examples 13-22 optionallycomprises: delivering a battery-powered implantable cardiac rhythmmanagement unit to an intra-body location; conductively coupling aninductive antenna to the implantable cardiac rhythm management device;generating the time-varying magnetic flux using the inductive antenna;and initiating a tissue electrostimulation using the implantable cardiacrhythm management unit.

In Example 24, the method of at least one of Examples 13-23 optionallycomprises: locating a distal end of an implantable flexible lead near tothe implantable wireless electrostimulation node; mechanically couplingthe inductive antenna to the distal end of the implantable flexiblelead; locating a proximal end of the cardiovascular implantable flexiblelead at or near to a housing of the battery-powered implantable cardiacrhythm management unit therapy control unit; locating at least twoantenna feed conductors within the implantable flexible lead;conductively coupling the at least two antenna feed conductors from thebattery-powered implantable cardiac rhythm management unit therapycontrol unit housing to the inductive antenna; and energizing the atleast two antenna feed conductors.

Example 25 describes a system. In this example, the system comprises:means for delivering a cardiovascular wireless electrostimulation nodeto an intra-body location; means for expanding a wirelesselectrostimulation node inductive pickup; means for generating atime-varying magnetic flux; means for linking the time-varying magneticflux to the wireless electrostimulation node inductive pickup; means forsurrounding a wireless electrostimulation node inductive pickup wireloop with a material of a relative magnetic permeability less than 1.1;means for capturing at least enough inductively-coupled energy todeliver a tissue electrostimulation;

means for controlling the initiation of the delivery of a specifiedtissue electrostimulation waveform; and means for delivering a specifiedtissue electrostimulation waveform in response to an initiation.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a diagram illustrating generally an example of at least aportion of a wireless electrostimulation system including a wirelessenergy transmission source, an implantable flexible lead comprising aninductive antenna, and multiple wireless electrostimulation nodesconfigured at cardiac sites.

FIG. 2 is a schematic diagram illustrating generally an example of atleast a portion of a wireless electrostimulation system including awireless energy transmission source and a wireless electrostimulationnode.

FIGS. 3A-B are views illustrating generally at least a portion of anexample of a wireless electrostimulation node included in a wirelesselectrostimulation system.

FIGS. 4A-B are similar to FIGS. 3A-B, but illustrate generally at leasta portion of another example of a wireless electrostimulation nodeincluded in a wireless electrostimulation system.

FIG. 5 is a partial cross-sectional view illustrating generally anexample of at least a portion of a wireless electrostimulation systemincluding a delivery catheter containing a wireless electrostimulationnode.

FIG. 6 is a partial cross-sectional view, similar to FIG. 5, butillustrating generally an example of at least a portion of a wirelesselectrostimulation system including the removal of a pull wire and theretraction of an actuator and delivery catheter.

FIG. 7 is a partial cross-sectional view illustrating generally anexample of at least a portion of a wireless electrostimulation systemincluding a wire loop and a mechanical support, showing a localencapsulant surrounding the wire loop and a bulk encapsulant surroundingboth the mechanical support and wire loop.

FIG. 8 is a diagram illustrating generally a perspective view of anexample of at least a portion of a wireless electrostimulation systemincluding a spiral wire loop wound coaxially to encircle a mechanicalsupport.

FIG. 9 is a diagram, similar to FIG. 8, but illustrating generally anexample of a perspective view of at least a portion of a wirelesselectrostimulation system including wire loop wound in a spiral on oneface of a mechanical support.

FIG. 10 is a diagram, similar to FIG. 1, but illustrating generally anexample of at least a portion of a wireless electrostimulation systemincluding an external device generating a time-varying magnetic flux.

FIG. 11 is a diagram illustrating generally an example of at least aportion of a process including a wireless stimulation node.

FIG. 12 is an example of a plot showing an analysis of the predictedoutput voltage developed at an example of a wireless electrostimulationnode inductive pickup receiver, and the corresponding actual outputvoltage when measured on a laboratory model, both plotted versus theseparation between an energy transmission source inductive antennatransmitter and wireless electrostimulation node inductive pickupreceiver.

FIG. 13 is an example of a plot from an efficiency analysis showing thecomputed power coupling efficiency and battery lifetime associated witha given separation between an example of an energy transmission sourceinductive antenna transmitter and an example of a wirelesselectrostimulation node inductive pickup receiver.

FIG. 14 is a diagram, similar to FIG. 1, but illustrating generally anexample of at least a portion of a wireless electrostimulation systemincluding a subcutaneous inductive antenna.

DETAILED DESCRIPTION

FIG. 1 is a diagram illustrating generally an example of at least aportion of a wireless electrostimulation system 100 including asubcutaneous implantable cardiac rhythm management unit 120, and animplantable flexible lead 106 coupled to an inductive antenna 108, andmultiple implantable wireless electrostimulation nodes 110A, 110B. FIGS.3A-B, 4A-B can be referred to for more detailed views of examples ofwireless electrostimulation nodes 110A, 110B.

The implantable wireless electrostimulation nodes, 110A, 110B, can beimplanted entirely within the heart, for example, at an endocardial sitealong the left ventricular free wall 102A and penetrating the myocardium102E. In the example of FIG. 1, the combination of the cardiac rhythmmanagement unit 120, flexible lead 106, and inductive antenna 108 can beconfigured as a wireless energy transmission source.

The wireless electrostimulation nodes or “seeds,” 110A, 110B, can beconfigured to receive inductively-coupled electromagnetic energy 114 asa time-varying flux generated by the inductive antenna 108. The energy114 is captured by expandable inductive pickups 112A, 112B coupled toeach seed 110A, 110B.

In the example shown in FIG. 1, the inductive antenna 108 can bedisposed at the distal end of the implantable flexible lead 106 such asto transmit energy 114 across the ventricular septal region 102B, withthe antenna 108 located near a fixation device 107. The fixation device107 can be located at or near the apical region 102C of the rightventricle.

In an example, the implantable flexible lead 106 can be configured withat least two internal antenna feed conductors. The antenna feedconductors can be electrically coupled to an implantable cardiac rhythmmanagement (CRM) device 120 through a header block 126A. The headerblock 126A can be used to mechanically and electrically couple one ormore leads such as 104, 106 to, for example, electronics, controlcircuitry, or a battery located within the cardiac rhythm managementdevice 120 therapy control unit housing 126B.

The CRM device 120 can be configured to wirelessly control initiation ortiming of electrostimulation via wireless seeds 110A, 110B. The CRMdevice 120 can also be configured to generate energy 114 and towirelessly communicate energy to the wireless seeds 110A, 110B such asfor use in providing electrostimulation. In certain examples, the CRMdevice 120 can also provide electrostimulation to one or more cardiacsites, such as near 102B, 102C, 102D, such as by using one or moretissue attachment or fixation devices 105, 107 respectively comprisingone or more conductive electrodes. The electrodes can be conductivelysupplied with electrostimulation energy, such as through one or morewires located internally to one or more of leads 104, 106.

In certain examples, one or more additional wireless stimulation nodes,such as 110A, 110B can be located in one or more other left heart 102regions, such as the left atrium or left ventricular septal region. Suchlocations within or associated with the left heart 102 can be used, forexample, in delivery of electrostimulation such as for cardiacresynchronization therapy, or to achieve conversion of atrial orventricular tachyarrhythmias through electrostimulation. In examplesinvolving one or more left-atrially associated seeds, similar to 110A,110B, a right-atrial flexible implantable lead 104, and fixation device105 can incorporate an inductive antenna 108, such as located in theatrial septal region, or one or more other atrial regions, such as 102D.In other examples, one or more other subcutaneous or external locationscan accommodate the wireless energy transmission source and inductiveantenna 108, including, for example, the vena cava, pericardial space,or esophageal space. FIG. 10 shows an example of an external wirelessenergy transmission source 1040.

In certain examples, control of initiation, timing, or delivery ofelectrostimulation is provided by the CRM device 120 comprising one ormore sensing electrodes 122A, 122B disposed on the housing 126B orheader 126A of the CRM device 120. The sensing electrodes 122A, 122Bcan, among other things, provide electrogram sensing of intrinsiccardiac activity, evoked response to electrostimulation, or parametersrelated to patient activity level (e.g., respiration, heart rate).Additionally, in another example, one or more fixation devices 105, 107can provide one or more sensing electrodes, and conductively couple oneor more sensed signals via leads 104, 106 to the CRM device 120.

In some examples, delivery of multiple seeds can allow defibrillation orcardioversion to be achieved using electrostimulation by the seeds,while decreasing, minimizing, or eliminating pain or patient discomfort.To achieve effective cardioversion or defibrillation, multiplere-entrancy paths within the cardiac tissue can be broken, orde-sensitized. The total delivered energy used to de-sensitize (e.g.,inhibit activation of) enough myocardium, 102E, for instance, can besubstantially larger if only a single defibrillation vector is used(e.g., a single pair of electrodes), compared to using multipledefibrillation sites.

FIG. 2 is a schematic diagram illustrating generally an example of atleast a portion of a wireless electrostimulation system 200 including awireless energy transmission source 220 and a wirelesselectrostimulation node (seed) 210.

The example in FIG. 2 shows a wireless energy source 220 that caninclude a battery 226, voltage regulator 225, and a microprocessor 224.In certain examples, the microprocessor 224 comprises input-output (I/O)capability such that a switching structure 228 can be coupled to themicroprocessor 224 to control current flow from the battery 226 or anoptional transient energy storage device such as a capacitor 227 to aninductive antenna 206. In one example, the inductive antenna iscomprised of a wire loop 208. In another example, the inductive antenna206 comprises of multiple wire loops 208 that can be configuredspatially orthogonal to one another such as to reduce orientationsensitivity. A tuning element 229 can be used to allow a range offrequencies to be selected at which a time-varying magnetic flux 214will be generated by the inductive antenna 206. The resultinginductance-capacitance (LC) circuit forms a resonant “tank” circuit,which can have an operable range of resonant frequencies selected from arange of 300 KHz to 10 MHz, but selected below the self-resonantfrequency of the inductor 208 comprising the inductive antenna 206.

Some examples of the tuning element 229 can include, but are notrestricted to, a capacitor, a variable-capacitance diode (“varicap”diode), an active circuit modeling a capacitor of a selected value, etc.In some examples, the switch 228 and tuning element 229 can be replaced,such as by a combination of a voltage-controlled oscillator and poweramplifier coupled to directly drive the inductive antenna 206 such as toachieve generation of magnetic flux 214 at a specified range offrequencies. The switch 228 can be realized either mechanically as amicrominiature relay device, or as solid-state device (e.g., FET, BJT,IGBT, SCR, or other thyristor). In some examples, the regulator 225,microprocessor 224, sensing circuit 223, and switching device 228 areco-integrated in a single integrated circuit or multi-chip modulepackage. Note that the term “microprocessor” can also include, amongother things, a microcontroller device including one or more of volatileor non-volatile memory, multiple input/output channels,analog-to-digital conversion devices, power supplies, ordigital-to-analog conversion devices that can be co-integrated in, forexample, a single integrated circuit, single circuit package, multi-chipmodule package, hybrid, polyimide flex-circuit assembly, etc.

In some examples, the initiation, timing, duration and frequency rangeof the generation of magnetic flux 214 is controlled by themicroprocessor 224 wherein the microprocessor 224 is provided with inputfrom a sensing circuit 223. The sensing circuit 223 can be coupled to,for example, wire leads 204A, 204B implanted subcutaneously withincardiac tissue 202A. In another example, the wireless energytransmission source can be external to the body, and leads 204A, 204Bcan be coupled to the skin of the patient (e.g., to measureelectrocardiograms). In the example shown in FIG. 1, the transmissionsource 220 can comprise one or more sense electrodes 222A, 222B coupledto the sensing circuit. In one example, sense electrodes 222A, 222B aredisposed on the housing of wireless energy transmission source 220.

The time-varying magnetic flux 214 may be generated for eithertransferring operating energy 214A to the seed device 210, or forcommunication 214B with the seed device 210 (e.g., one range offrequencies can be established for wireless energy transfer, and asecond range of frequencies can be established for commanding the seeddevice 210 to deliver stimulus).

In the example shown in FIG. 2 filter 209 can discriminate between power214A and communication 214B signaling. For example, filter 209 can beconfigured to detect a particular range of frequencies of time-varyingflux 214B captured by the seed 210 such as by using an inductive pickup212. The filter 209 can be coupled to stimulus control logic 216. Logic216 can be configured to either inhibit or to initiate tissueelectrostimulation, such as in response to the filter 209 detecting aspecified signal. Filter 209 can include, in certain examples, aband-pass filter, which can be coupled to a threshold comparator. Incertain examples, the filter 209 can include a digital demodulator. Insome examples, communication signal 214B can be encoded digitally andtransmitted concurrently to, or comprising, power signal 214A. Examplesof digital encoding of communication signal 214B can include, but arenot restricted to, on-off keying, amplitude-shift keying, phase-shiftkeying, frequency-shift keying, or the like.

In some examples, the combination of the capacitance of the tuningelement 229 and actual or parasitic capacitances of the inductiveantenna 206 can vary when the wireless energy transmission source isimplanted in or near tissue 202E. The effect of tissue interaction withthe system can be reduced by at least partially surrounding theinductive antenna 206 or inductive pickup 212 (see, e.g., FIG. 7) with aprotective material or encapsulant. Such encapsulation can inhibit orprevent tissue 202E or liquid penetrating into the cavities betweenindividual turns of a multi-turn inductive pickup 212 or inductiveantenna 206, which would otherwise increase the effective relativedielectric constant seen by the pickup 212, or antenna 206.

In some examples, the microprocessor 224 can be configured to adjust thecapacitance of the tuning element 229, or to adjust the frequency of acorresponding voltage-controlled oscillator, such as to achieve adesired level of efficiency in coupling to the implanted seed 210. In anexample, cardiac pacing electrostimulus can be applied using electrodes250 and 260, and the evoked response can be observed using eithersensing electrodes 205A, 205B, 222A, 222B or an externalelectrocardiogram sensing apparatus. Tuning element 229, or acorresponding frequency synthesizer, can be adjusted by microprocessor224, such as to vary the range of frequencies of magnetic flux 214 thatare generated, for example, until a desired or reliable “capture,”(e.g., activation of cardiac tissue resulting from electrostimulation)is observed.

The seed device 210 can include an inductive pickup 212 and an optionaldiscrete tuning element 211. In an example, the value of the capacitanceof element 211 can be selected before implant of the seed device, suchas to achieve a desired resonant frequency when implanted, such assurrounded by blood or muscle tissue. In some examples, to reduce thesize of the seed device 210, a discrete capacitor 211 can be omitted,and the capacitance used to achieve resonance of the inductive pickup212 can be the parasitic capacitance of the physical coil structure ofthe inductive pickup 212 (for example, the inter-winding capacitance).

Inductively-coupled energy 214A can be rectified, such as by a full-waverectifier 213, as shown in the example in FIG. 2, or by a half-waverectifier, which can save space by reducing the number of diodecomponents used in the seed device 210. Rectified energy can be storedin an optional energy storage device 215, such as shown in the examplein FIG. 2. In an example, the energy storage device 215 can act like afilter capacitor, such as to help suppress ripple voltage. Stimuluscontrol logic 216 can be coupled to a switch device 217. The switch 217can include a solid-state device (e.g., FET, BJT, IGBT, SCR, thyristor,etc.). In an example, such as to reduce the size of the seed 210, thefilter 209, logic 216, switch 217, and rectifier 213 can beco-integrated into a single integrated circuit package, or for example,into a multi-chip module, etc. similar to that described above in thecontext of the wireless energy source 220.

In some examples, multiple storage devices 215 and switches 217 can beused, such as to arrange stored voltages in a desired series, parallel,or series-parallel combination, such as to achieve an electrostimuluspeak voltage in excess of the maximum voltage stored on a single storagedevice 215 using the power signal 214A.

A direct-current (DC) blocking device 218 can be used to inhibit aDC-stimulus component from being coupled to electrostimulus electrodes250, 260. Electrostimulus electrodes 250, 260 can be conductivelycoupled to the muscle tissue 202E to be electrostimulated (e.g.,myocardial tissue). In an example, electrode 250 can be used as thecathode electrostimulation electrode, and electrode 260 can be used asthe anode electrostimulation electrode.

The blocking device 218 and the shunt device 219 can form a high-passnetwork configured such that the upper cutoff frequency and resultingtime-domain pulse shape can be selected or even programmably adjustedsuch as to form a desired electrostimulus waveform. In an illustrativeexample, blocking device 218 can be selected as a capacitor havingcapacitance of about 1 microFarad, and shunt device 219 can be selectedas an approximately 5 kiloOhm resistor to achieve a desired cardiactissue electrostimulation pacing pulse.

The present inventor has recognized that, among other things, tissue andbody fluid inductive energy absorption and dispersive effects canrapidly increase at frequencies greater than 100 KHz. These effects canseverely limit the range and maximum achievable efficiency of typicalmagnetic coupling schemes. One technique for decreasing the lossesinduced by such effects can be to substantially or completely surroundthe inductors 208, 212 with a high relative permeability magneticmaterial such as an iron-powder core or a ferrite material or the like.Such materials can magnify the magnetic flux density seen by woundstructures nearby them, at a given incident magnetic field intensity.

The high relative magnetic permeability of such materials can render theresultant implantable device assemblies incompatible with magneticresonance imaging (MRI) equipment. Forces or torques induced locally(e.g., induced in single components) associated with the strong biasfield present near operating MRI equipment could result in mechanicaldamage to the inductive antenna 206 or inductive pickup 212 assembliesif they incorporate a high relative magnetic permeability material.

Additionally, operating MRI equipment can induce large voltages acrossthe terminals of the inductive antenna 206 or inductive pickup 212, andlarge currents inducing an internal temperature rise. These effects canresult in irreversible damage (e.g., electrical short-circuiting ordielectric failure) to the inductors 208, 212 or to other componentselectrically coupled to the inductors 208, 212, and possibly thermaldamage to surrounding tissue 202E.

Additional protection devices (e.g., discharge tubes, gaps, solid-statetransient-suppression devices) can be included to inhibit or preventMRI-related electrical damage. In the case of the seed device 210, smallsize is generally desired (e.g., to allow intravascular introduction andplacement) and such additional protection devices can take up additionalspace and could fail to mitigate the MRI-induced forces and torques.

The present inventor has also recognized, among other things, thatferrite core materials can also have limitations. For example, internalloss mechanisms can preclude their usage as core materials forhighly-tuned inductors at frequencies in excess of a few MHz. Thisprevents the resonant “tank circuits” in the inductive transmit network,229, 208 and inductive receiver network 212, 211, from achieving highpower coupling efficiencies, since the Quality factors (“Q”) of bothnetworks are limited by the resistive damping effects of increasinglosses within the ferrite core material.

By contrast, the present inventor has recognized that, in a differentapproach, the core materials or mechanical supports surrounding theinductive antenna 206 or inductive pickup 212 can be selected to have arelative magnetic permeability less than 1.1, and can be comprised ofone or more materials other than ferrites, or the core material ormechanical support can provide the antenna 206 or the pickup 212 with aneffective relative magnetic permeability substantially equal to 1 (suchas by using a non-magnetic material, such as air, blood, bodily tissue,bodily fluid, or one or more other materials for the core material orthe mechanical supports).

Materials, such as shape-memory Nickel-Titanium (NiTi or Nitinol)compounds, are effectively non-ferromagnetic and can have otherbeneficial mechanical properties. For example, the shape-memory propertycan be used to expand (e.g., after implant) a loop antenna 206 orinductive pickup 212. By increasing or maximizing the area of a loopforming an inductive antenna 206, or inductive pickup 212, the mutualcoupling of two such inductive devices in proximity can be enhanced.Such materials can also help mitigate ferrite efficiency loss and allowmore efficient coupling of time-varying magnetic flux through tissue,such as at frequencies up to several MHz. The term “air core” can beused to describe the inductive transmitter 208 and receiver 212structures, even though the actual construction of such devices mightinclude non-ferromagnetic metallic support structures and, whenimplanted, tissue or bodily fluid may be present within the core of theinductive transmitter 208 or receiver 212.

A mathematical analysis of a simplified combination of the wirelessenergy source 220 and seed 210 allows power coupling efficiency, η, andelectrostimulus output voltage magnitude, |V_(L)|, to be computed. Thecombination of switch 228, and battery 226 can be represented as an ACvoltage source operating at angular frequency ω, and peak output voltageV₀. The inductive antenna 206 can be modeled as a combination of anideal inductor 208, as L, in series with a transmit circuit resistanceR. Tuning element 229 can be modeled as a capacitor, C. The transmitcircuit impedance can be represented as Z=R+i (ωL−1/ωC), in which i=√−1.At resonance, C=1/ω²L, and Z=R. The imaginary components, due to thereactances of the capacitor and inductor, can cancel each other (unitypower factor).

Similarly, for the circuitry included in seed 210, the inductor 212 canbe modeled as L₁, and its corresponding loss as resistance “r” in serieswith L₁. Tuning element 211 can be modeled as a parallel capacitor C₁,and the tissue load 202E appearing across electrostimulus electrodes250, 260 can be modeled as R_(L). Neglecting the rectifier 213, switch217, shunt capacitor 215, blocking device 218, and shunt resistor 219,the receiver inductive pickup impedance can be represented as Z₁=r+iωL₁and the impedance associated with the tissue load and tuning element canbe represented as Z_(L)=R_(L)/(1+iωR_(L)C₁).

For the seed 210, this corresponds to a lossy inductive pickup Z₁=r+iωL₁in parallel with a load comprised of Z_(L)=R_(L)/(1+iωR_(L)C₁). Thetotal parallel impedance Z₂=r+R_(L)/(1+(ωR_(L)C₁)²)+i[ωL₁−ωR_(L)²C₁//(1+(ωR_(L)C₁)²]. At resonance, 1+(ωR_(L)C₁)²=ωL²C₁/L₁, andZ₂=r+R_(L)/(1+(ωR_(L)C₁)²)=r[1+L₁/(rR_(L)C₁)]. The magnitude ofZ_(L)=√(L₁/C₁).

The mutual inductance, M, of transmit antenna 206 and inductive pickup212 can be represented as the product of the self inductances of the twoinductors 208, 212 and a coupling constant, κ: M²=κL L₁. Power couplingefficiency and peak output voltage at the tissue load 202E can berepresented as:

η=κQQ _(1X)/[(1+x)(1+x+κQQ ₁)]  (1)

|V _(L)=√{square root over ((R _(L) /R)κQQ _(1X))}V ₀/(1+xκQQ ₁)   (2)

where Q=ωL/R=quality factor of transmitter, Q₁=ωL₁/r=quality factor ofreceiver, and x=L₁/(rR_(L)C₁). The following relation can be obtained:

κQQ ₁>>1+x, η→x/(1+x)   (3)

and when x>>1, the power coupling efficiency, η, approaches 1(corresponding to 100%). Thus, for small values of the couplingconstant, κ, if the quality factors are sufficiently large, the powercoupling efficiency can approach unity.

Generally, the seed 210 receiver resonant frequency and quality factorQ₁ can vary depending on the specific implant configuration of theinductive pickup 212, and the resulting tissue and blood proximityeffects on the electrical response of the inductive pickup 212. However,by actively statically or dynamically varying the value of tuningelement 229 in the wireless energy source 220, as described previously,the wireless energy source 220 transmitter resonant frequency can bevaried, such as to compensate for changes in the seed 210 receiverresonant frequency or to control electrostimulus amplitude or energyachieved at electrodes 250, 260.

If the transmitter 220 quality factor, Q, is selected to be much greaterthan the receiver quality factor, Q₁, the receiver can have a broader“tuning envelope” than the transmitter. With a broader seed 210 receiverresponse characteristic, the transmitter tuning element 229 can beadjusted more easily (e.g., less precisely) to provide an operatingfrequency at resonance corresponding the to resonant frequency of thereceiver in seed 210 (e.g., the transmitter can be tuned to be moresharply “peaked” at resonance than the receiver, and transmitterresonant frequency can then be swept until centered on receiver resonantfrequency).

In some examples, varying the resonant frequency of the transmitter bychanging the capacitance of tuning element 229 can also control themagnitude of the electrostimulus voltage coupled to the tissue load202E. Selecting a value for tuning element 229 that shifts the resonantfrequency of the wireless energy source 220 away from the resonantfrequency of the seed 210 can result in decreasing maximum voltage,|V_(L)|, coupled to the tissue load 202E. This can reduce the size ofthe seed 210 by eliminating or reducing the complexity of logic 216 andthe switch device 217 such as by allowing electrostimulation amplitudecontrol to be accomplished by the wireless transmission source 220.

In some examples, power signal 214A can be limited in duration ormaximum amplitude such as to avoid tissue heating or regulatory limitsfor average or instantaneous power transmitted through tissue. Theresulting rectified energy can be integrated or otherwise accumulatedby, for example, storage device 215. |V_(L)| can, for instance, beestablished by a series- or shunt-regulation component such as a Zenerdiode 230.

In some examples, Zener diode 230 can be used to simplify or eliminatestimulus control logic 216 and switch device 217 when a pulse-widthmodulation (PWM) scheme is used at the transmission source 220. Amicroprocessor, state machine, timing logic, and the like can be omittedfrom the seed 210 to reduce complexity, physical volume, etc.

In one example, stimulus control logic 216 can still be used to inhibitelectrostimulation delivery to tissue load 202E (e.g., by opening switchdevice 217 when an intrinsic event is sensed), but is not required tocontrol the level of electrostimulation energy content delivered totissue load 202E.

In some examples, power signal 214A can be established at a specificburst duration (e.g., a burst can be a square pulse envelope commencinga sequence of multiple resonant oscillations). The duration or pulsewidth of the burst of power signal 214A can be related to the energycontent delivered to the tissue load 202E when the regulation device 230is clamping the voltage across the storage device 215.

If tissue 202E is modeled as a cardiac tissue load having a resistanceR_(L)=1 kiloOhm in parallel with a series-combination of a 1 kiloOhmresistor (r_(L)) and a 1 microFarad capacitor (C_(L)), a cardiac tissueelectrostimulation pacing pulse of greater than 4V peak amplitude,|V_(L)|, can be achieved using a resonant frequency of 1 MHz.

For the leading edge of an example of a cardiac tissueelectrostimulation pulse, the load capacitor can be representedeffectively as a short circuit, and the AC resistance of the modelcardiac tissue load 202E is equal to around 500 ohms (1 kiloOhm inparallel with 1 kiloOhm).

In some examples, the burst duration of power signal 214A can becontrolled by the microprocessor 224 and switching element 228 at thetransmission source 220 to achieve a desired energy content coupled tothe tissue load 202E.

A theoretical voltage delivered across a cardiac tissue capacitance,V_(CAP), can be represented as:

V _(CAP) =V _(CLAMP)[1−e ^(−w/r) _(L) ^(C) _(L)]  (4)

where V_(CLAMP) represents the voltage clamping threshold of theregulating device 230, and w represents the burst pulse duration (inseconds). For small burst pulse durations, V_(CAP) can be approximatedas:

V _(CAP) =V _(CLAMP) [w/r _(L) C _(L)] for w<<r_(L) C _(L)   (5)

In an example, V_(CLAMP) can be 5.6V (e.g., established by a Zener diode230), w can be 775 microseconds, r_(L)=R=1 kiloOhm, and C=1 microFarad.Using EQUATION 4, V_(CAP) can be computed as approximately 3 Volts. Inanother example, w can be 1250 microseconds, and V_(CAP) can be computedas approximately 4 Volts.

In some examples, the volume occupied by seed 210 can be decreased bylimiting the total energy stored, for example, storage device 215. Anestimate of the desired stored energy for various electrostimulationpulses can be made. For example, if R_(L)=500 Ohms, and |V_(L)|=2.5V, asquare-wave pulse of duration T=0.4 milliseconds can correspond to astored electromstimulation energy of T|V_(L)|²/R_(L)=5 microJoules.

Storage device 215 can be specified as a capacitor=C_(S), inmicroFarads. The energy stored in capacitor 215 can be represented as ½C_(S)|V_(L)|². The number of electrostimulation delivery cycles that theenergy stored in the capacitor 215 can deliver can be represented as:the energy stored on the capacitor=½ C_(S)|V_(L)|², divided by theelectrostimulation energy consumed by a single electrostimulation cycledelivered to the tissue impedance=T|V_(L)|²/R_(L). Thus, the number ofcycles that capacitor 215 can supply can be representedas=R_(L)C_(S)/2T.

Tradeoffs can be made between storage device 215 value C_(S), loadresistance R_(L) and, for example, pulse width, to achieve a desiredseed 210 volume and a desired electrostimulation duration, for instance,during an interval when inductive power signal 214A can be inhibited.

For example, the number of desired electrostimulation cycles can be=N,and the capacitor value for storage device 215 to provide Nelectrostimulation cycles can be represented as C_(S)=2TN/R_(L). In anexample, an electrostimulation pulse duration can be specified as T=0.4msec, the load resistance can be R_(L)=500 Ohms, and the capacitanceC_(S) can be represented for N=1 as C_(S)=1.6 μF. A low voltage 1.6 μFcapacitor 215 can be small (e.g., sub-millimeter dimensions on eachaxis).

In some examples, back-up storage can be desired for patient protection(e.g., to provide continued electrostimulation for a limited duration inthe temporary absence of power signal 214A). A heart rate can bespecified=H_(R) in Hertz, a number of cardiac cycle to be paced in atotal time=T_(stored), in seconds, can be represented=H_(R)T_(stored),and the size of the capacitor to store a corresponding amount of energycan be represented, C_(S)=2TH_(R)T_(stored)/R_(L). For example, onehour=3600 sec of stored electrostimulation energy and a heart rate of 72beats per minute or 1.2 Hz can be specified, resulting in, for example,a number of pacing electrostimulation cycles H_(R)T_(stored)=4320, and atotal stored energy=21.6 milliJoules. The tissue impedance R_(L) can bespecified as 500 Ohms and pulse width can be specified as T=0.4 msec,and the capacitance 215 can be represented C_(S)=6912 μF. Such acapacitor can occupy several cubic millimeters of volume in the receivercircuit.

In some examples, a compromise between capacitor 215 value C_(S) and thephysical size of the capacitor 215 can be made. For example, a capacitor215 can be specified, C_(S)=320 μF, and electrostimulation pulses can bespecified, |V_(L)|=2.5 volts.

In an example, the total energy stored on capacitor 215 is 1 milliJoule,and can be enough energy to deliver 200 electrostimulation cycles ofpulse width T=0.4 msec to into a tissue load R_(L)=500 Ohms. In anexample, capacitor 215 can be specified C_(S)=320 μF and theelectrostimulation cycle rate of 72 electrostimulation cycles per minutecan result in continued electrostimulation delivery, for approximately2.8 minutes, by seed 210, after energy 214A input to C_(S) is inhibited.

Capacitor 215 can also be specified to accommodate the quiescent powerconsumed by, for example, stimulus control logic 216 comprising amicroprocessor, which can be very small depending upon the device used,but in some cases can be comparable to, or larger than, the averagepacing power. In some examples, the power consumed by the receivercircuit 210 can be reduced if stimulus control logic 216 and filter 209are omitted and switch 217 is permanently closed or omitted. For someexamples, the capacitor C_(S) can be a filter capacitor, and the energy214A received by the seed 210 is rectified and delivered directly to thetissue load (e.g., the delivered electrostimulation pulse width cancorrespond to the width of a transmitted energy 214A burst pulse,provided that the time constant τ=C_(S)R_(L) is less than about one halfof the pulse width). In some examples, direct conversion of energy 214Ainto an electrostimulation delivery can be achieved and C_(S)<0.4 μF canbe specified (e.g., corresponding to an electrostimulation pulse widthof T=0.4 msec and load R_(L)=500 Ohms).

In some examples, sensing circuitry 232 can be coupled to cardiac tissue202E to provide signaling to stimulus control logic 216 in response tosensed potentials detected by the sensing circuitry 232. Signaling tostimulus control logic 216 can occur in response to intrinsic tissueactivity (e.g., sensing circuitry 232 establishes a threshold level orwindow and intrinsic activity can cause a voltage fluctuation exceedinga threshold level or window). Stimulus control logic 216 can inhibitelectrostimulation using switch 217 in response to, for example,detection of sensed events provided by sensing circuitry 232.

In some examples, a shunt device 219 can also provide chargeneutralization. Charge neutralization can include providing a pathbetween the electrostimulus electrodes 250, 260 to slowly discharge anafterpotential occurring during or after an electrostimulation,resulting in a net neutral charge delivered by the electrostimulationelectrodes 250, 260. For the example of a pacing waveform describedabove, charge neutralization can be observed as a smaller amplitudenegative-phase pulse of longer duration following the positive-phasecardiac tissue electrostimulation pulse.

FIGS. 3A-B are views illustrating generally at least a portion of anexample of a wireless electrostimulation node 110A or “seed” that can beincluded in a wireless electrostimulation system. Wirelesselectrostimulation node 110A can be configured as a cardiovascularwireless electrostimulation node fixed to or in myocardial tissue 102.Inductive energy can be coupled to an inductive pickup 112 supported byone or more shape-memory or other mechanical struts 300A, 300B, 300C,300D. In an example, as shown in FIG. 3B, the struts 300A, 300C, 300Dcan be disposed radially around the cylindrical housing 310 such as atangles of 120 degrees with respect to each other. FIG. 7 shows anexample of a partial cross section view of the inductive pickup 112comprising both a mechanical support and a separate inductive wire loop,attached to the mechanical support. In another example, the inductivepickup wire loop itself can serve as both the electrical pickup andmechanical support, reducing the complexity of the assembly.

In some examples, a tissue attachment mechanism such as helical fixationdevice 255 can secure a cylindrical housing 310 to myocardial tissue102. This can pull the cylindrical housing 310 to a desired depth withinmyocardial tissue 102 such as with an objective of leaving as little ofthe housing 310 protruding out of the myocardial tissue 102 as possible.This can reduce or minimize the possibility of impingement against othertissue such as during a heart contraction. The total length of the seed110A can be selected to reduce or minimize the likelihood of penetratingthe far side of the myocardium 102.

In an example, assuming a nominal minimum myocardial wall thickness of10 mm, the cylindrical housing 310 can be configured to have a diameterof less than or equal to 2 mm, and a length of less than or equal to 5mm, such that a total length of the cylindrical housing 310 plus theanode 260, cathode 250, and fixation device 255 is less than 10 mm,which is short enough to avoid piercing the far side of the myocardium.In some examples, discrete internal electronic components can beincluded in the cylindrical housing 310. Housing 310 internal electroniccomponents can be selected for reduced size, and can include, amongother things, one or more discrete surface-mount capacitors, discretesurface-mount resistors, or discrete surface-mount diodes, and the like.In an example, a single diode can be used as a half-wave rectifier toreduce housing 310 volume.

A cathode electrode 250 can provide a first electrostimulation electrodethat can be embedded into myocardial tissue 102. In certain examples,all or a portion of fixation device 255 can be conductively coupled toelectrode 250 such as to target electrostimulation to a specific depthof myocardial tissue 102. An anode electrode 260 can provide a secondelectrostimulation electrode that can be in contact with either othercardiac tissue 102 or blood, for instance to provide a return path tocomplete the electrostimulation circuit.

For example, in an endocardial application, the cardiovascular wirelesselectrostimulation node 110A is configured for intravascular delivery tothe interior of the heart, via one or more blood vessels, such astransluminally through a lumen of a catheter, and can be embedded inmyocardium 102 penetrating an endocardial wall 102A such as the leftventricular free wall. Blood in contact with anode 260 can provide aconductive path for electrostimulation energy allowing contractileelectrostimulation (e.g., pacing) of the myocardium 102 coupled tocathode 250.

In some examples, a retainer shaft 265 can be included, such as to allowfor manipulation of the seed 110A during implantation (for instance, tosecure an actuator assembly to the seed 110A as part of an intravasculardelivery system).

Struts 300A-D can be constructed from a spring-like (e.g.,self-expanding or self-opening) flexible shape-memory material such as aNiTi (Nitinol) compound, such as to accommodate a desired insertiondepth of the cylindrical housing while flexibly maintaining anapproximately circular loop shape for inductive pickup 112. In someexamples, struts 300A-D can be welded or adhered to an inductive pickup112 comprising a mechanical support made of a shape-memory material suchas a NiTi (Nitinol) compound.

FIGS. 4A-B are similar to FIGS. 3A-B, but illustrate generally at leasta portion of another example of a wireless electrostimulation node 110Bthat can be included in a wireless electrostimulation system. Thecombination of one or more struts 400A-D or barb structures 455A-B canprovide fixation of the seed 110B in, for example, cardiac tissue 102.In these examples, rotation is not required in order to establish aspecified depth of penetration in myocardium 102. Housing 410 can bepushed into tissue 102 to a desired depth, such as to avoid piercing anepicardial wall opposite penetration into the myocardium 102. In theexample in FIGS. 4A-B, the housing 410 is shown as cylindrical, but theactual cross-section of the housing can also be configured as a polygonsuch as to inhibit or to prevent rotation within an implant deliverycatheter.

Implant depth can be controlled or limited such as by modifying strutstructures 400A-D to provide a “J”-shaped loop or hook extendingoutwards from housing 410 as shown in the example of FIG. 4A. As theseed 110B further penetrates myocardium 102, eventually struts 400A-Dcan limit further insertion (e.g., insertion force increasessubstantially as “J”-shaped loops impact heart wall 102A). Side barbs455A-B can be included such as to inhibit or prevent removal of seed110B without substantial force. In this manner, specified depth can beobtained or maintained. In some examples, barbs 455A-455B can beconfigured to expand outward or retract inward, such as duringimplantation, such as to facilitate one or more of implantation, removalor retraction of seed 110B.

A variety of different electrostimulus electrode shapes can be used,including, for example, a point-type cathode electrode 450 such as shownin FIG. 4A, and a corresponding anode electrode 460.

Struts 400A-D can be mechanically secured to inductive pickup 112B, suchas by wrapping around or encircling the cross section of inductivepickup 112B, for example, such as shown in FIG. 4A. Other techniques ofmechanically coupling struts 400A-D can include welding or adhering oneor more of the struts 400A-D, such as to one or more of the housing 410,inductive pickup 112B, etc.

Generally, a retainer shaft 465 can be provided, such as to temporarilysecure the seed 110B to an actuator component of an intravasculardelivery system during implant.

In some examples, one or more elements of the seeds 110A and 110B shownin FIGS. 3A, 3B, 4A, 4B can be coated with an anti-coagulant or othertreatment, such as to suppress clot or thrombus formation. In someexamples, one or more elements of the seeds 110A, 110B can be finishedwith a surface treatment, such as to enhance tissue ingrowth. In someexamples, the seed 110A, 110B can be incorporated into the tissue 102.Such embedding can reduce the likelihood of thrombo-embolism, and canalso reduce the threshold energy that achieves desiredelectrostimulation (e.g., reduction of myocardial pacing thresholdvoltage).

Examples of tissue ingrowth enhancing treatments include surfaceroughening or texturing, or one or more other porosity-enhancementtreatments. Examples of elements that can be treated with a tissueingrowth enhancing surface finish include the strut structure(s) 300A-D,400A-D, the inductive pickup 112A or 112B, cylindrical housing 310 or410, etc.

In certain examples, one or more elements of the seeds 110A and 110B caninclude one or more materials that can be selected for radio-opacity,such as to enhance visibility of an implanted component duringradiographic medical imaging.

FIG. 5 is a partial cross-sectional view illustrating generally anexample of at least a portion of a wireless electrostimulation systemincluding an elongate intravascular delivery catheter 570, such as forcarrying or passing a wireless electrostimulation node housing 510through a lumen 571 formed by the catheter 570.

In some examples, venous access can be achieved via the subclavian veinor femoral artery, and a guide catheter can then be inserted. Forexample, once a guide catheter has achieved access to an endocardialregion of the heart 102A, a delivery catheter 570, for example as shownin FIG. 5, can be passed transluminally through the lumen of the guidecatheter. The delivery catheter 570 can be open at an end near a cardiactissue target 102. The delivery catheter 570 can be large enough inhollow cross sectional area forming the lumen 571 to allow acardiovascular wireless electrostimulation node housing 510, expandableinductive pickup 512 and one or more expandable struts 500A, 500B to berouted through one or more blood vessels via the catheter 571 andendocardially implanted entirely within the heart at the tissue target102.

The rotational position and position along the length of the deliverycatheter 570 of the seed housing 510 can be manipulated, in an example,such as by a hollow, flexible actuator 572. The actuator 572 can bemechanically coupled to a retainer pin 565 that can be connected to theseed housing 510. A fingered-adaptor 574 can be used to engage theretainer pin 565 and to displace it into a corresponding recess on thefingered-adaptor 574 such as by using a locking wire 573.

At the distal end of the delivery catheter, outside the body, a plungeror other similar manipulator can be used, such as to apply rotational ortranslational (e.g., sliding) force to actuator 572. For example, if ahelical tine fixation device 555 is used, the actuator 572 can transmitrotational force to the seed housing 510 to screw the tine 555 intomyocardial tissue 102, such as to achieve a desired depth duringimplantation of the seed housing 510.

During the implant procedure, one or more struts 500A, 500B can be usedto couple the inductive pickup 512 to the mechanical housing 510 of theseed. The struts 500A, 500B can be delivered in folded or compressedform, such as to reduce cross-sectional area during delivery. In anexample, such as shown in FIG. 5, the struts 500A, 500B and inductivepickup 512 can be folded linearly parallel to the body of the housing510. In another example, to further reduce the net length of the entireassembly during implant, the struts 500A, 500B and inductive pickup 512can be wound spirally around the housing 510. Once a desired depth offixation device 555 is achieved, locking pull-wire 573 can be pulled.For example, if attached to an independent manipulator at the distal endof the delivery catheter 570, pull-wire 573 can be removed by pullingthe manipulator. Once locking pull-wire 573 has been pulled clear ofretainer pin 565, the entire delivery catheter 570 and actuator rod 572can be pulled away from cardiac tissue wall 102A. This allows seedhousing 510, and fixation 555 to remain.

FIG. 6 is a partial cross-sectional view, similar to FIG. 5, butillustrating generally an example of at least a portion of a wirelesselectrostimulation system including the removal of a pull-wire 573, theretraction of an actuator rod 572 and fingered-adaptor 574 through thehollow region, such as a lumen 571, of a delivery catheter 570, and theretraction of the catheter 570 from a cardiac tissue wall 102A. In thisexample, retainer pin 565 is no longer captive, thus seed assembly 110Cremains at the cardiac tissue location 102A, 102.

In some examples, when delivery catheter 570 is pulled away from cardiactissue wall 102A, inductive pickup 512 can expand to an outer diameterof, for instance, 2 centimeters. The size of the inductive pickup 512when folded, as shown in FIG. 5, can be related to the size of theinductive pickup 512 when expanded, as shown in FIG. 6. The expandedouter diameter of inductive pickup 512 can be selected to allow forintravascular delivery using delivery catheter 570.

Once clear of the hollow region, such as the lumen 571, of the deliverycatheter 570, shape-memory mechanical struts 500A, 500B can expand theinductive pickup 512, such as by using a self-expanding shape-memorymaterial. In an example, additional expansion force and shape-memory canbe provided by the inductive pickup 512 itself comprising a mechanicalsupport that can be separate from the struts 500A-B. See FIGS. 7-9 forexamples of inductive pickup and inductive antenna configurations.

Similar to FIGS. 3A-B, and FIGS. 4A-B, fixation device 555 can helpretain the seed 110C, such as at a specified depth in myocardial tissue102. Anode 550 and cathode 560 electrodes provide electrostimulusenergy.

FIG. 7 is a partial cross-sectional view illustrating generally anexample of at least a portion of a wireless electrostimulation systemincluding an inductive assembly 700. In this example, the inductiveassembly 700 includes windings of a wire loop 710A, 710B and amechanical support 705. In this example, a local encapsulant 720 can beprovided, such as for surrounding the wire loop windings 710A, 710B. Abulk encapsulant 730 can be provided, in certain examples, such as forsurrounding both the mechanical support 705 and wire loop windings 710A,710B. The cross-sectional view of the assembly 700 can describe eitheran inductive pickup included as a portion of a seed device (such asshown in FIG. 3A-B), or, for example, to an inductive antenna includedas a portion of a wireless energy source (such as shown in FIG. 1).

In the example shown in FIG. 7, multiple windings 710A, 710B can bedisposed adjacent to or near a mechanical support 705. The windings710A, 710B can be constructed of flexible insulated wire. Individualwindings 710A, 710B, can themselves be constructed of multiple strandsof non-insulated wire, such as for providing enhanced flexibility. In anexample, Litz wire (e.g., comprising multiple strands of silver wire)can be selected, such as for providing flexibility and improved magneticperformance, such as discussed below with respect to the example of FIG.12. In another example, insulated silver wire can be used for one ormore of the wire loops 710A, 710B.

In the example shown, encapsulant 720 can serve to inhibit or preventblood or moisture ingress into the inter-winding areas betweenindividual wire loops 710A, 710B. The encapsulant 720 can also helpadhere winding loops 710A, 710B together, such as to preserve therelative spacing and position of the winding loops 710A, 710B.Preventing moisture ingress and stabilizing the windings can help reducevariation in electrical performance, such as over time or during implant(e.g., the inductance and inter-winding capacitance of the inductiveassembly can remain more stable).

To facilitate expansion during implantation, the encapsulant 720 can beselected for elasticity, such as for flexibility, or forbio-compatibility, such as if no bulk encapsulant 730 is used. Amaterial for encapsulant 720 such as medical-grade silicone can provideboth elasticity and bio-compatibility.

In certain examples, the bulk encapsulant 730 can serve both to protectthe inductive pickup assembly 700 and to secure the inductive wire loops710A, 710B to mechanical support 705. Examples of bulk encapsulants caninclude bio-compatible overmolding compound, heat-shrink tubing,silicone, or other materials that can be selected for flexibility andbio-compatibility. The outer-most exposed surface of the inductiveassembly 700, in the example shown in FIG. 7 the bulk encapsulant 730,can be treated with either a substance that promotes a tissue ingrowth,or an anti-coagulation substance or both, similar to such finish ortreatment such as discussed with respect to FIGS. 3A-B, 4A-B. Theencapsulant can include a variety of possible over-molding or sheathingmaterials. The encapsulant need not result in an entirely void-freespace. For example, the encapsulant can permit penetration of one ormore other elements of the assembly 700. For instance, in some examples,one or more strut structures such as described in previous figures, canpenetrate the encapsulant material 730, such as to achieve mechanical orother affixation to the mechanical support 705. In certain examples,such a strut structure can be mechanically or otherwise affixed to theencapsulant material 730. In certain examples, a porous or roughenedouter surface can be intentionally developed on the encapsulant material730, such as to promote tissue ingrowth. In certain examples, only asingle insulated wire winding loop 710A is used without any separatesupport 705.

FIG. 8 is a diagram illustrating generally a perspective view of anexample of at least a portion of a wireless electrostimulation systemincluding a spiral wire loop 802 wound coaxially to encircle amechanical support 800 or “core.” In this example, a non-conductive gapor discontinuity 801 is located along the mechanical support loop 800.The gap 801 can reduce a loss induced by a “shorted secondary effect” ofthe core 800 when a conductive material is used for the core 800. Such aloss can be due to induced eddy currents in, for example, the mechanicalsupport loop 800. The shorted secondary effect occurs when the core 800acts like a shorted transformer winding magnetically coupled to the wireloop 802. The electrical effect of such losses can include reducedefficiency or de-tuning of the high-Q inductive antenna/inductive pickuppair in operation. This can be referred to as “antenna pulling.”Introducing gap 801 breaks up the induced current loop formed by thecore 800 and can reduce loss or antenna pulling effects.

FIG. 9 is a diagram, similar to FIG. 8, but illustrating generally aperspective view of an example of at least a portion of a wirelesselectrostimulation system including wire loop 902 wound in a spiral on aface of a mechanical support 900, and including a non-conductive gap901, similar to that discussed above with respect to FIG. 8. Theexamples shown in FIGS. 8-9 demonstrate that different physicalarrangements of inductive wire loops 802, 902 can be used, such as withrespect to mechanical supports 800, 900. In some examples, FIGS. 8-9 canbe combined with the encapsulant or surface treatments discussed in FIG.7, such as to form a bio-compatible inductive antenna or inductivepickup assembly capable of being implanted within an endocardiallocation or within the coronary vasculature.

FIG. 10 is a diagram, similar to FIG. 1, but illustrating generally anexample of at least a portion of a wireless electrostimulation system1000 including an external device 1040 configured for generating atime-varying magnetic flux 1014 that can be captured by one or moreimplantable wireless electrostimulation nodes 1005A, 1005B at a cardiaclocation 102 inside a patient body 1010. For example, the externaldevice 1040 can be a physician programmer unit comprising a therapycontrol unit and wireless energy transmission source. In certainexamples, the external device 1040 can include a device worn externallyby a patient, such as to provide ambulatory electrostimulation therapyon demand or according to a program established by the external device1040. In certain examples, such as where acute electrostimulationtherapy is desired (e.g., in conjunction with percutaneous coronaryintervention or other related treatment), the external device 1040 canbe incorporated into a bed, vest, hat, chair, or other apparatus thatcan be worn by or located near the patient, such as for the brief periodduring which electrostimulus therapy is desired.

FIG. 11 is a diagram illustrating generally an example of at least aportion of a process 1100 that can be performed including a wirelesselectrostimulation node. In certain examples, the wirelesselectrostimulation node can be delivered to a location 1105 within apatient's body. An inductive pickup can be expanded at the location1110,such as using a self-expanding material, or using one or moremanipulators, such as passed through a catheter delivery system as shownin FIGS. 5-6. Magnetic flux can be generated by a separate inductiveantenna and linked to the inductive pickup 1115. The resulting voltageinduced in the inductive pickup results in energy capture 1120. Thecaptured energy can be stored or delivered immediately or upon command.In certain examples, such as shown in FIG. 11, the wirelesselectrostimulation node can wait for a command to initiate tissueelectrostimulation 1125, such as a command from a therapy control unit.Upon receipt of the command, the wireless electrostimulation node thendelivers tissue electrostimulation 1130. In some examples, the commandand time-varying magnetic flux providing energy for electrostimulationcan be the same (e.g., providing nearly instantaneous electrostimulationupon receipt of an appropriate magnetic-flux signal, for instance withina specified range of frequencies, or for a specified duration, such asdescribed above with respect to FIG. 2).

FIG. 12 is a plot showing an example of an analysis of an outputvoltage, (“Vcalc”), predicted at a wireless electrostimulation nodeinductive pickup receiver. A corresponding actual measured outputvoltage, (“Vmeas”) can be measured across the output electrodes of aninductive pickup receiver of an experimental prototype of the wirelesselectrostimulation node. The measured output voltage, (“Vmeas”),corresponds to the peak voltage measured on the rising edge of aelectrostimulation waveform measured across the wirelesselectrostimulation node's electrostimulation electrodes, which arecoupled to a test load.

Both voltages (“Vcalc,” “Vmeas”) can be plotted versus the separation(e.g., in centimeters) between (1) an energy transmission sourceinductive antenna (transmitter) and (2) a wireless electrostimulationnode inductive pickup (receiver).

The materials and electrical parameters used for constructing by way ofexample the experimental prototype described with respect to FIG. 12 aredescribed in TABLE 1. The calculated predicted output voltage shown inFIG. 12, (“Vcalc”), can be estimated by computing |V_(L)| using EQUATION2 and the electrical parameters shown in TABLE 1.

TABLE 1 Electrical and Mechanical Parameters Tested for an Example Shownin FIG. 12. Wireless Energy 5 cm diameter circular coil made with 10turns of Transmission AWG#25 insulated copper. Source Total measuredseries transmitter resistance (coil, FET (Transmitter): driver, andcapacitor resistances): R = 2.4 Ohms in EQUATION 2. Measured transmitterinductance L = 11.5 μH Measured transmitter circuit Q = 30.3 Inputvoltage amplitude V₀ = 7.2 Volts (at 1 MHz switched on for 500 uSduration at a repetition rate of 1.2 Hz corresponding to a nominal 72beat-per-minute pacing rate). Wireless 1.7 cm diameter circular coilmade with 7 turns of Electro- 0.005″ silver Litz wire. Litz wirecomprising 6 stimulation parallel strands of insulated 0.002″ silverwire Node Measured receiver resistance r = 0.33 Ohms (Receiver):Measured receiver inductance L₁ = 2.0 μH Measured and computed receiverinductance Q₁ = 39 Tuning capacitor C₁ = 0.0116 μF Load: R_(L) = 500Ohms for calculation. Actual test load is a 1 kOhm resistor in parallelwith a series-combina- tion of a 1 kOhm resistor and 1 uF capacitor.

FIG. 13 is an example of a plot from an efficiency analysis showing thenumerically estimated power coupling efficiency, η, in percent (%), andbattery lifetime (in months) associated with a given separation between(1) an example of an energy transmission source inductive antenna(transmitter) and (2) an example of a wireless electrostimulation nodeinductive pickup (receiver)

The power coupling efficiency, η, can be computed from EQUATION 1, suchas using the electrical parameters of TABLE 1. Assuming an outputvoltage of |V_(L)|=3.6 Volts at a coil separation of, for example, 8 cm,as a pacing benchmark, the output power can be computed as|V_(L)|²/(2R_(L))=˜0.013 Watts for the duration of the pacing pulse.

The average power output can by computed by multiplying this value bythe duty cycle. An example of a cardiac pacing pulse duration is 500μsec, and an example of a cycle length is 850 msec (corresponding to ˜70heart beats per minute). The resulting duty cycle is 0.00059, and theaverage output power for a 3.6 volt pacing amplitude is around 7.5 μW.

The input power can be computed by dividing the computed output power,for this example 7.5 μW, by the power coupling efficiency, η, computedfrom EQUATION 1, and adding the quiescent power consumed by, forexample, a microprocessor or microcontroller in the transmitter. Such aquiescent power can be, in an illustrative example, 0.425 μW. Assuming aminimum 3.6 volt pacing amplitude, FIG. 12 shows power couplingefficiencies, η, in percent (%), for a range of separations between thetransmitter and receiver coils assuming electrical parameters as arespecified in the example in TABLE 1.

Dividing a battery Watt-hour capacity by the output power usage gives anestimate of the battery lifetime. An example of a 25-gram lithiumrechargeable battery includes around 12 Watt-hours of useful(recoverable) energy. FIG. 13 shows battery lifetime (in months) forvarious separations between transmitter and receiver coils assumingelectrical parameters as specified in the example in TABLE 1 andassuming, in an illustrative example, a 12 Watt-hr charge available toan implantable transmitter battery.

In the example shown in FIG. 13, battery lifetimes of around threemonths or longer can be feasible for receiver separations of 8 cm orless at pacing output voltages of 3.6 volts or less.

Received power will diminish as the angle between the planes of thetransmit and receive coils deviates from zero degrees (reducing thecoupling coefficient, κ), resulting in orientation sensitivity. In someexamples, multiple transmit coils in multiple planes, and even multiplecoils in a single plane, can help reduce such orientation sensitivity.Multiple receiver coils consume little additional energy in the farfield of the transmitter, allowing for examples in which multiplereceivers can operate near an inductive transmitter.

In certain examples, such as discussed above, a useful range of 8 cm canbe suitable for a transmitter inductive antenna that can be placedagainst the right ventricular (RV) septum with one or more loopreceivers that can be located endocardially on the left ventricular (LV)free wall, for example, even for a dilated heart. In some examples, aninductive receiver on the apical LV free wall can be separated by 4-6 cmfrom a transmitter in the RV or an external transmitter.

FIG. 14 is a diagram, similar to FIG. 1, but illustrating generally anexample of at least a portion of a wireless electrostimulation systemincluding a subcutaneous inductive antenna. In some examples, animplantable transmitter inductive antenna 1408 need not be locatedendocardially within a heart 102, and may be placed subcutaneously onthe chest of a patient 1010, or in the pericardial space adjacent to theheart 102.

An inductive antenna feedwire assembly 1406 can be electrically coupledbetween (1) an inductive antenna 1408 at a distal end of the feedwireassembly 1406, and (2) an implantable cardiac rhythm management device1420 at a proximal end of the feedwire assembly 1406. In some examples,an inductive antenna 1408 generates a time-varying magnetic flux to becaptured by electrostimulation electrode assemblies 1005A, 1005B.

In some examples, the inductive antenna 1408 and feedwire assembly 1406can be constructed similarly to, for example, an endocardial flexiblelead system (e.g., a bio-compatible silicone outer jacket can beselected for an outer surface of the feedwire assembly 1406, and one ormore coiled metallic conductors insulated from one another can be usedinternally to the assembly 1406 to energize an inductive antenna 1408).

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown and described. However, the present inventors alsocontemplate examples in which only those elements shown and describedare provided.

All publications, patents, and patent documents referred to in thisdocument are incorporated by reference herein in their entirety, asthough individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “a” or “one or more.” In this document, the term“or” is used to refer to a nonexclusive or, such that “A or B” includes“A but not B,” “B but not A,” and “A and B,” unless otherwise indicated.In the appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein.” Also, in the following claims, the terms “including” and“comprising” are open-ended, that is, a system, device, article, orprocess that includes elements in addition to those listed after such aterm in a claim are still deemed to fall within the scope of that claim.Moreover, in the following claims, the terms “first,” “second,” and“third,” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, the code may be tangibly stored on one ormore volatile or non-volatile computer-readable media during executionor at other times. These computer-readable media may include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. (canceled).
 2. A wireless electrostimulation system, comprising: awireless electrostimulation seed configured to be implantedendocardially entirely within a heart chamber of a patient's heart, thewireless electrostimulation seed comprising: a body having a proximalend and a distal end; a tissue attachment mechanism positioned proximatethe distal end of the body, the tissue attachment mechanism configuredto secure the body to cardiac tissue; a first electrostimulationelectrode configured to contact cardiac tissue when the body is securedto cardiac tissue; a second electrostimulation electrode spaced from thefirst electrostimulation electrode; a rechargeable power source; tissueelectrostimulation circuitry operably coupled to the firstelectrostimulation electrode and the second electrostimulationelectrode, the tissue electrostimulation circuitry being powered atleast in part by the rechargeable power source; a receive antenna forwirelessly receiving recharge energy; and recharge circuitry operativelycoupled to the receive antenna and the rechargeable power source, therecharge circuitry configured to recharging the rechargeable powersource using recharge energy received via the receive antenna; asubcutaneously implantable therapy device comprising: a housing; atransmit antenna configured to be located subcutaneously within thepatient; a battery situated in the housing; charge circuitry operativelycoupled to the transmit antenna and the battery; and wherein the chargecircuitry is configured to causes the transmit antenna to send rechargeenergy to the receive antenna of the wireless electrostimulation seed.3. The wireless electrostimulation system of claim 2, wherein thesubcutaneously implantable therapy device comprises a lead extendingfrom the housing, and wherein the transmit antenna is incorporated intothe lead.
 4. The wireless electrostimulation system of claim 3, whereinthe lead comprises at least two antenna feed conductors disposedinternally to the lead and operatively coupled to the transmit antenna.5. The wireless electrostimulation system of claim 3, wherein thetransmit antenna is disposed at a distal end of the lead.
 6. Thewireless electrostimulation system of claim 3, wherein the lead is anelectrostimulation lead for delivering electrostimulation therapy to thepatient's heart.
 7. The wireless electrostimulation system of claim 2,wherein the charge circuitry is configured to provide a time-varyingsignal to the transmit antenna to send the recharge energy to thereceive antenna.
 8. The wireless electrostimulation system of claim 2,wherein the transmit antenna, the receive antenna, the charge circuitryand/or the recharge circuitry is/are configured to produce a resonantcoupling between the transmit antenna and the receive antenna.
 9. Thewireless electrostimulation system of claim 8, wherein the resonantcoupling has a resonant frequency that is within a range of frequenciesfrom 500 kilohertz to 5 megahertz, and has a power coupling efficiencyof at least 1%.
 10. The wireless electrostimulation system of claim 2,wherein the first electrostimulation electrode is a cathode and thesecond electrostimulation electrode is an anode.
 11. The wirelesselectrostimulation system of claim 10, wherein the tissueelectrostimulation circuitry is configured to generate, between theanode and the cathode, an electrostimulation pulse of at least 2.5V peakamplitude at a pulse width of 0.4 msec when coupled to a 500 Ohmequivalent load.
 12. A wireless electrostimulation system, comprising: awireless electrostimulation seed configured to be implantedendocardially entirely within a heart chamber of a patient, the wirelesselectrostimulation seed comprising: a body having a proximal end and adistal end; a tissue attachment mechanism positioned proximate thedistal end of the body, the tissue attachment mechanism configured tosecure the body to cardiac tissue; a first electrostimulation electrodeconfigured to contact cardiac tissue when the body is secured to cardiactissue; a second electrostimulation electrode spaced from the firstelectrostimulation electrode; a rechargeable power source; tissueelectrostimulation circuitry operably coupled to the firstelectrostimulation electrode and the second electrostimulationelectrode, the tissue electrostimulation circuitry being powered atleast in part by the rechargeable power source; a receive antenna forwirelessly receiving recharge energy; recharge circuitry operativelycoupled to the receive antenna and the rechargeable power source, therecharge circuitry configured to recharging the rechargeable powersource using recharge energy received via the receive antenna; asubcutaneously implantable therapy device comprising: a housing; atransmit antenna; a battery situated in the housing; charge circuitryoperatively coupled to the transmit antenna and the battery; and whereinthe charge circuitry is configured to causes the transmit antenna tosend recharge energy to the receive antenna of the wirelesselectrostimulation seed; and wherein the transmit antenna, the receiveantenna, the charge circuitry and/or the recharge circuitry is/areconfigured to produce a resonant coupling between the transmit antennaand the receive antenna with a power coupling efficiency of at least 1%,and the resonant coupling has a resonance frequency that is within arange of frequencies from 500 kilohertz to 5 megahertz.
 13. The wirelesselectrostimulation system of claim 12, wherein the subcutaneouslyimplantable therapy device comprises a stimulation lead extending fromthe housing having one or more simulation electrodes, and wherein thetransmit antenna is incorporated into the stimulation lead.
 14. Thewireless electrostimulation system of claim 13, wherein the stimulationlead comprises at least two antenna feed conductors disposed internallyto the stimulation lead and operatively coupled to the transmit antenna.15. The wireless electrostimulation system of claim 13, wherein thetransmit antenna is disposed at a distal end of the stimulation lead.16. A wireless electrostimulation system, comprising: a wirelesselectrostimulation seed configured to be implanted endocardiallyentirely within a heart chamber of a patient, the wirelesselectrostimulation seed comprising: a body having a proximal end and adistal end; a tissue attachment mechanism positioned proximate thedistal end of the body, the tissue attachment mechanism configured tosecure the body to cardiac tissue; a first electrostimulation electrodeconfigured to contact cardiac tissue when the body is secured to cardiactissue; a second electrostimulation electrode spaced from the firstelectrostimulation electrode; a rechargeable power source; tissueelectrostimulation circuitry operably coupled to the firstelectrostimulation electrode and the second electrostimulationelectrode, the tissue electrostimulation circuitry being powered atleast in part by the rechargeable power source; a receive antenna forwirelessly receiving recharge energy; recharge circuitry operativelycoupled to the receive antenna and the rechargeable power source, therecharge circuitry configured to recharging the rechargeable powersource using recharge energy received via the receive antenna; asubcutaneously implantable therapy device comprising: a housing; astimulation lead extending from the housing having one or moresimulation electrodes; a transmit antenna, wherein the transmit antennais incorporated into the stimulation lead; a battery situated in thehousing; charge circuitry operatively coupled to the transmit antennaand the battery; and wherein the charge circuitry is configured tocauses the transmit antenna to send recharge energy to the receiveantenna of the wireless electrostimulation seed.
 17. The wirelesselectrostimulation system of claim 16, wherein at least part of thestimulation lead extends subcutaneously within the patient, and thetransmit antenna is located along the part of the stimulation lead thatextends subcutaneously within the patient.
 18. The wirelesselectrostimulation system of claim 16, wherein the stimulation leadcomprises at least two antenna feed conductors disposed internally tothe stimulation lead and operatively coupled to the transmit antenna.19. The wireless electrostimulation system of claim 16, wherein thecharge circuitry is configured to provide a time-varying signal to thetransmit antenna to send the recharge energy to the receive antenna. 20.The wireless electrostimulation system of claim 19, wherein the transmitantenna, the receive antenna, the charge circuitry and/or the rechargecircuitry is/are configured to produce a resonant coupling between thetransmit antenna and the receive antenna.
 21. The wirelesselectrostimulation system of claim 20, wherein the resonant coupling hasa resonant frequency that is within a range of frequencies from 500kilohertz to 5 megahertz, and has a power coupling efficiency of atleast 1%.